[flang] Catch branching into FORALL/WHERE constructs

[klausler]

Summary

Enforce constraints C1034 & C1038, which disallow the use
of otherwise valid statements as branch targets when they
appear in FORALL &/or WHERE constructs. (And make the
diagnostic message somewhat more user-friendly.)

[klausler]

ping

[rovka]

Shouldn't you add new testcases with forall and where (and while you're at it, maybe also with select and the others that aren't covered by these 4 tests)?

flang/lib/Semantics/resolve-labels.cpp

230

Nitpick: I think this tuple was sorted alphabetically before.

[klausler]

Address comments from Diana P.

[rovka]

LGTM, thanks.

flang/lib/Semantics/resolve-labels.cpp

       std::is_same_v<A, parser::EndWhereStmt>) {
     // Executable construct end statements are also supported as
     // an extension but they need special care because the associated
-    // construct create there own scope.
+    // construct create their own scope.
     return Legality::formerly;
   } else {
     return Legality::never;

         parser::BlockStmt, parser::ChangeTeamStmt, parser::CriticalStmt,
         parser::IfThenStmt, parser::NonLabelDoStmt, parser::SelectCaseStmt,
         parser::SelectRankStmt, parser::SelectTypeStmt>;
-    using LabeledConstructEndStmts =
-        std::tuple<parser::EndAssociateStmt, parser::EndBlockStmt,
-            parser::EndChangeTeamStmt, parser::EndCriticalStmt,
-            parser::EndDoStmt, parser::EndIfStmt, parser::EndSelectStmt>;
+    using LabeledConstructEndStmts = std::tuple<parser::EndAssociateStmt,
+        parser::EndBlockStmt, parser::EndChangeTeamStmt,
+        parser::EndCriticalStmt, parser::EndDoStmt, parser::EndIfStmt,
+        parser::EndSelectStmt, parser::EndForallStmt, parser::EndWhereStmt>;
     using LabeledProgramUnitEndStmts =
         std::tuple<parser::EndFunctionStmt, parser::EndMpSubprogramStmt,
             parser::EndProgramStmt, parser::EndSubroutineStmt>;

     return SwitchToNewScope();
   }
   bool Pre(const parser::WhereConstruct &whereConstruct) {
-    return PushConstructNameWithoutBlock(whereConstruct);
+    return PushConstructName(whereConstruct);
   }
   bool Pre(const parser::ForallConstruct &forallConstruct) {
-    return PushConstructNameWithoutBlock(forallConstruct);
+    return PushConstructName(forallConstruct);
   }
 
   void Post(const parser::AssociateConstruct &associateConstruct) {

   void Post(const parser::SelectTypeConstruct &selectTypeConstruct) {
     PopConstructName(selectTypeConstruct);
   }
-
   void Post(const parser::WhereConstruct &whereConstruct) {
-    PopConstructNameWithoutBlock(whereConstruct);
+    PopConstructName(whereConstruct);
   }
   void Post(const parser::ForallConstruct &forallConstruct) {
-    PopConstructNameWithoutBlock(forallConstruct);
+    PopConstructName(forallConstruct);
   }
 
   // Checks for missing or mismatching names on various constructs (e.g., IF)

     }
     return PushSubscope();
   }
-  template <typename A> bool PushConstructNameWithoutBlock(const A &a) {
-    const auto &optionalName{std::get<0>(std::get<0>(a.t).statement.t)};
-    if (optionalName) {
-      constructNames_.emplace_back(optionalName->ToString());
-    }
-    return true;
-  }
-
-  template <typename A> void PopConstructNameWithoutBlock(const A &a) {
-    CheckName(a);
-    PopConstructNameIfPresent(a);
-  }
   template <typename A> void PopConstructNameIfPresent(const A &a) {
     const auto &optionalName{std::get<0>(std::get<0>(a.t).statement.t)};
     if (optionalName) {

     } else if (!InInclusiveScope(scopes, scope, target.proxyForScope)) {
       // Clause 11.1.2.1 prohibits transfer of control to the interior of a
       // block from outside the block, but this does not apply to formats.
+      // C1038 and C1034 forbid statements in FORALL and WHERE constructs
+      // (resp.) from being branch targets.
       if (target.labeledStmtClassificationSet.test(
               TargetStatementEnum::Format)) {
         continue;
       }
       context.Say(position,
-          parser::MessageFormattedText{
-              "Label '%u' is not in scope"_en_US, SayLabel(label)});
+          "Label '%u' is in a construct that prevents its use as a branch target here"_en_US,
+          SayLabel(label));
     }
   }
 }

flang/test/Semantics/label05.f90

-
 ! RUN: not %flang_fc1 -fdebug-unparse-with-symbols %s 2>&1 | FileCheck %s
 ! CHECK: Label '50' was not found
-! CHECK: Label '55' is not in scope
+! CHECK: Label '55' is in a construct that prevents its use as a branch target here
 ! CHECK: Label '70' is not a branch target
 ! CHECK: Control flow use of '70'
 

flang/test/Semantics/label06.f90

-
 ! RUN: not %flang_fc1 -fdebug-unparse-with-symbols %s 2>&1 | FileCheck %s
-! CHECK: Label '10' is not in scope
+! CHECK: Label '10' is in a construct that prevents its use as a branch target here
 ! CHECK: Label '20' was not found
 ! CHECK: Label '30' is not a branch target
 ! CHECK: Control flow use of '30'
-! CHECK: Label '40' is not in scope
-! CHECK: Label '50' is not in scope
+! CHECK: Label '40' is in a construct that prevents its use as a branch target here
+! CHECK: Label '50' is in a construct that prevents its use as a branch target here
 
 subroutine sub00(n)
   GOTO (10,20,30) n

flang/test/Semantics/label07.f90

-
 ! RUN: not %flang_fc1 -fdebug-unparse-with-symbols %s 2>&1 | FileCheck %s
 ! CHECK: Label '30' is not a branch target
 ! CHECK: Control flow use of '30'
-! CHECK: Label '10' is not in scope
+! CHECK: Label '10' is in a construct that prevents its use as a branch target here
 ! CHECK: Label '20' was not found
 ! CHECK: Label '60' was not found
 

flang/test/Semantics/label14.f90

 !            Block Construct
 
 ! RUN: %flang_fc1 -fsyntax-only %s 2>&1 | FileCheck %s
-! CHECK: Label '20' is not in scope
+! CHECK: Label '20' is in a construct that prevents its use as a branch target here
 
 subroutine s1
   block